This invention relates to adhesion promoters. More particularly, this invention relates to improved adhesion promoters suitable for use in room temperature vulcanizable silicone compositions.
One component room temperature vulcanizable (RTV) silicone rubber compositions are frequently used as protective coatings and as encapsulation coatings. Such applications require that the bond between the RTV silicone composition and substrate on which it is coated be as strong as possible.
During the course of development of one component RTV silicone rubber compositions, it became desirable for such compositions to contain self-bonding additives, i.e., adhesion promoters, which would allow the RTV composition to bond without a primer to various types of substrates with good adherency. Such adhesion promoters are disclosed, for example, in U.S. Pat. No. 4,483,973 (Lucas et al.) and 4,863,992 (Wengrovius et al.).
U.S. Pat. No. 4,483,973 to Lucas et al. (Lucas '973) discloses a one component RTV silicone rubber composition containing an adhesion promoter which is a silane functionalized by radicals selected from amino, ether, epoxy, isocyanato, cyano, acryloxy, and acyloxy. U.S. Pat. No. 4,863,992 to Wengrovius et al. (Wengrovius) discloses a one component RTV silicone rubber composition containing an adhesion promoter which is selected from the group consisting of N-trialkoxysilylalkyl-substituted amides and imides, N-mono(trialkoxysilylalkyl)-substituted ureas, N,N'-bis(trialkoxysilylalkyl)-substituted ureas, trialkoxysilylalkyl isocyanurates and mono-(N-trialkoxysilylalkyl)alkylenediamines.
The present invention is based on the discovery that an adhesion promoter which provides better adhesion than those disclosed in the Lucas '973 and Wengrovius patents discussed above can be obtained by reacting certain of the adhesion promoters disclosed in those patents with certain silanol fluids, the resulting reaction product then being used as the adhesion promoter in the RTV silicone composition.
RTV compositions containing the polysiloxane adhesion promoters disclosed in the Lucas '973 and Wengrovius patents referenced above and silanol fluids which can be used in the present invention are disclosed, for example, in copending, commonly assigned application Ser. No. 07/628,776 (Lucas), filed on Dec. 17, 1990; and U.S. Pat. Nos. 4,593,085; 4,895,918, both to Lucas. However, these references do not teach the use of the reaction product of the polysiloxane adhesion promoting compound and the silanol fluid as the adhesion promoter and do not suggest that such a reaction product will be a superior adhesion promoter to the polysiloxane adhesion promoters taught in those references as well as in U.S. Pat. No. 4,483,973 to Lucas et al.